But there was a catch. Finding a single gene was painstakingly difficult.
Finding
many genes working in combination was technologically impossible at the time.

Imagine that you unravel the spiraling double-helix ladder of human DNA and stretch
the rungs out flat on a highway. (The technical term for a rung is a base pair,
two linked amino acids called nucleotides.) Each of the 80,000 or so human genes is
a code made up of anywhere from a few hundred to tens of thousands of base pairs,
interspersed with sections of non-coding DNA. Chromosome 21 stretches along for
37 million rungs.

Finding a mutated version of a few of those base pairs would be like finding a
single address along an unknown road, somewhere in North America, without a map.

Fast-forward to 1996

he map that someday may guide the way to answers about
Down syndrome and other inherited diseases is being made at startling speed. Cox is
one of the cartographers, along with other scientists at Stanford and more than 100
institutions and private companies, racing to chart out the 3 billion base pairs of
the human DNA ladder. Halfway through the 15-year, $3 billion federally funded
Human Genome Project, the partial maps theyve assembled have led to the discovery
of hundreds of genes.